Currently, in the semiconductor industry there is a great interest in the characterization of thin films. Integrated circuits are made up a large number of thin films deposited onto a semiconductor substrate, such as silicon. The thin films include metals to make connections between the transistors making up the chip, and dielectric films to provide insulation between the metal layers (see: S. A. Campbell, The Science and Engineering of Microelectronic Fabrication, Oxford University Press, (1996)). The metal films (interconnects) are typically arranged as a series of patterned layers. At the present time there may be 4 or 5 layers of interconnects. It is likely that as more complex integrated circuits are developed which will require a greater number of interconnections the number of layers will increase. Metals of current interest include, for example, aluminum, copper, titanium and silicides. Insulating films include, for example, oxide glasses of various compositions and polymers.
A metal film will contain crystal grains with a distribution of sizes and orientations. The range of sizes may be narrow or broad, and a distribution of grain sizes may have a maximum at some size and then decrease monotonically as the size increases or decreases. Alternatively, there may be a bi-modal distribution so that there is a high concentration of grains in two different ranges of size. The grain size affects the mechanical and electrical properties of a metal film. Consequently, in the semiconductor industry there is a strong interest in finding techniques that can monitor the grain size in metal films.
In the semiconductor device fabrication industry, it is important that a method for grain size determination be non-destructive, be able to measure the grain size within a small area of film, and give results in a short period of time. Current techniques for the determination of grain size include; measurement of the width of the peaks in intensity of diffracted X-rays, electron microscopy and atomic force and scanning tunneling microscopy. These techniques cannot meet the combined requirements listed above.